METHOD OF EVALUATING THE CORROSION RATE OF METAL

摘要

A metal test piece is disposed in a cell filled with a test solution. The metal test piece is electrically charged instantaneously through a counter electrode so as to have a few millivolts polarization potential ?t. The charge consumed by the corrosion reaction of the test piece is measured by a potential recorder in the form of a variation of the polarization potential ?t with respect to time t. The measured (?t-t) relation is analyzed to obtain the polarization resistance Rp of the metal test piece. After the potential of the metal test piece returns to its natural potential Ecorr, the test piece is charged again until its polarization potential ?t rises to 50 millivolts or more, and the (?t-t) relation is measured in the same way as mentioned above. Based on this relation, the Tafel slop .beta.a of the anodic reaction is obtained. After the potential of the metal test piece-has returned to its natural potential Ecorr, the test piece is so charged fro the third time as to have its polarization potential ?t lowered to -50 millivolts or less, and the (?t-t) relation is measured. This relation is analyzed to obtain the Tafel slope .beta.c of the cathodic reaction. Based on the polarization resistance Rp, Tafel slopes .beta.a and .beta.c, the corrosion current density Icorr is obtained, from which the density corrosion rate V is calculated.